The present invention relates to a novel coated superabrasive grit which is useful for producing improved abrasive or cutting tools. The present invention also includes within its scope the tools thus produced embodying the coated grit.
Superabrasives grit such as diamond and CBN, attached to a supporting body, is widely used for removing materials. Typical applications include, for example, sawing, drilling, dressing, grinding, lapping and polishing.
In typical applications, the grit is held in a suitable matrix and attached to a tool body. The retention of the grit is primarily accomplished by mechanical means, such as by surrounding the grit with the matrix material. This method of attachment, although simple and practical, has limitations because the exposure of the grit must be limited so as not to weaken the mechanical grip of the surrounding matrix. As a result, the cutting rate is limited by the small grit exposure. Further, as the matrix is worn down, the retention becomes insufficient so the grit can be "pulled out" and lost. For example, in a typical saw blade application, the average exposure of the diamond grit is less than 20% of the total grit height, and the grit is often lost due to the pull-out when it is worn down to about 1/3 of its original size. After using this saw blade for some time, typically about 1/3 of the original grit is lost as evidenced by the empty pockets on the blade.
In order to overcome this problem, coating of grit has be attempted to improve the bonding strength. U.S. Pat. No. 3,650,714 to Farkas describes a process for applying such coating on a diamond grit. Typical commercially available coated superabrasives products include DeBeer Co.'s titanized products for saw grit and General Electric Co.'s titanized products for CBN grit. For all metal matrix superabrasives tools the only commercially available coating for grit is titalized products.
However, it has been found that titanized products, particularly for diamond grit, are not effective in improving the attachment strength. The performance evaluation i.e. life & cutting rate of titanized grit in saw blade applications did not show noticeable improvement. One problem encountered by the titanized product is its lack of resistance against oxidation. It is well known that Ti or TiC can be oxidized in most saw blade manufacturing conditions. The oxidation can destroy the bonding between the grit and coating material, and between the coating material and the matrix. The other problem titanized products faced is the thinness of the coating. Titanized products typically contain less than 1 micron thick of Ti or TiC. Such a thi" coating can not prevent the dissolution or removal of the coating from the grit surface by the matrix material during rhe manufacturing process for tools. U.S. Pat. Nos. 3,757,878 and 3,757,879 to Wilder describe an encapsulation method for diamond particles. However, this is directed to produce a mechanical envelope for the grit and no chemical bonding is achieved.